Nicholas,
It's a two step process:
I know how to add excluded folders to a capture action
(1) The first step is to do just that. Open your capture actions and add the file or folders you want excluded to the Filter section of the capture action.
In the QRecall Help (Delete Item) it tells you how to delete items from an archive
(2) Then do that; open the archive, select the item(s) you excluded in step 1 and choose the Archive > Delete Item... command.
Step 2 removes all traces of that item from the archive, and step 1 prevents those items from being recaptured.